This invention relates to an electrolyte for electrolytic capacitors, and more particularly to an amate salt electrolyte and to a process for preparing the electrolyte salts in situ in the electrolyte solution used in the capacitors.
A prior art electrolyte system containing a solute of an ammonium or amine salt of an amic acid or amate was described by Ross et al in U.S. Pat. No. 4,117,531 issued Sept. 26, 1978. The amic acids and their salts were prepared by reacting the anhydride with ammonia or amines in ether. Reaction of the cyclic anhydrides, e.g. succinic, maleic, phthalic or hexahydro phthalic anhydride, with ammonia or a primary or secondary amine lead to formation of succinamic acid, maleamic acid and phthalamic acid, respectively. Reaction of these "amic" acids with a second equivalent of ammonia or with a primary or secondary or tertiary amine produces the amate salts. The resulting isolated salts and amic acids were used in formulating electrolytes in the conventional solvents used in capacitor electrolytes. The resulting electrolytes were suitable for use in capacitors at low and intermediate voltages up to 200 V.
Another prior art electrolyte system was described by Ross et al in U.S. Pat. No. 4,454,567 issued June 12, 1984 wherein the solvent was a mixture of an aprotic solvent and glycol. The preferred aprotic solvents were N-methylpyrrolidinone (NMP) and .gamma.-butyrolactone (BLO), both capable of acting as acceptors in hydrogen bonding, but not as donors. Whereas glycol can function as both acceptor and donor in hydrogen bonding.